It has long been recognized that wire reinforced flexible hose can be modified so that the helical wire serves as an electrical conductor as well as a structural member. This is particularly useful in vacuum cleaner devices where an electrically operated component such as a brush at the remote end of the hose receives its power through the hose wall rather than through a separate conductor. See for example U.S. Pat. No. 2,890,264.
More recently, a design of such a hose has been proposed with two parallel helical wires, each insulated with plastic, and with a single ply wall of flexible plastic disposed about the wire convolutions. Such a double lead structure is shown in U.S. Pat. Nos. 3,636,285 and 3,928,715. Hose of this form is typically somewhat stiff and has less than satisfactory abrasive resistance, particularly on the raised convolutions over the wires. A certain degree of added strength is provided in another form of prior art hose where a side-by-side pair of insulated helical wires are covered by two uniformly thick plastic wall plies with helical and longitudinal reinforcing cords between the plies. This is a single lead, rather than a double lead, structure and hence the total amount of wire is quite large, resulting not only in added weight but in increased voltage drop as well.
The double-wire single lead hose referred to has been manufactured on a continuously advancing definite length mandrel device as shown in U.S. Pat. No. 3,155,559, in which a helical belt forms the mandrel surface. This mandrel device has itself been modified as described in a pending application, Ser. No. 903,772, filed May 10, 1978, entitled "Continuously Advancing Mandrel" and it is characterized by two belts wound side by side to form the mandrel surface. Each time the mandrel turns once a point on its surface advances a distance equal to two belt widths in a double lead manner. This new mandrel makes possible the manufacture of improved double wire hose designs of which the present invention is one.